Field of the Invention
The present disclosure relates to an imaging device manufacturing method.
Description of the Related Art
Metal impurities such as iron and nickel may be mixed into a substrate for an imaging device such as a complementary metal-oxide semiconductor (CMOS) sensor in a process of manufacturing the imaging device. The metal impurities, particularly heavy metal impurities, electrically activated in the silicon substrate may cause white flaws as one of the characteristics of the imaging device due to the fixed charge.
Japanese Patent Application Laid-Open No. 2012-129312 discusses a process of directly forming a polysilicon film on a lower surface of a substrate. The polysilicon film formed on the back surface of the silicon substrate functions as a film for capturing (gettering) the metal impurities mixed in the process of manufacturing the imaging device in a region away from an active region.
In addition, Japanese Patent Application Laid-Open No. 2012-129312 also discusses forming a protective film on the polysilicon film formed on the back surface of the substrate to prevent the polysilicon film formed on the back surface of the substrate from being removed in a process of removing the polysilicon film formed on the front surface of the substrate. For example, the protective film for protecting the polysilicon film is an insulating film made of a silicon oxide film formed, for example, by a thermal oxidation method or a low-pressure (LP) thermal chemical vapor deposition (CVD) method (LPCVD method).
On the other hand, Japanese Patent Application Laid-Open No. 2012-182426 discusses forming an insulating film functioning as an antireflection film for light incident on a photoelectric conversion unit in a pixel region and simultaneously forming an insulating film on a side wall of a gate electrode of a transistor disposed in a peripheral circuit region. In this case, the insulating film is formed not only on the front surface side of the substrate but also on the back surface side of the substrate.